Gigabit upload speeds very slow

Hi all - I am having very slow upload speeds on my Gigabit extra internet service.  I just ran two tests (one of them was Xfinity's) and upload speeds were just under 8mbps.  My download speed isn't that great either, with a top-of-the-line desktop computer connected directly to the router by ethernet getting only 872mbps (instead of 1200mbps).  Any tips?  It seems like it has slowed down in recent weeks, but not sure.  I've not changed anything or added any devices lately.  Thanks.